Method for oxide insulating aluminum conductors



M. F. SMITH Feb. 25, 1958 METHOD FOR OXIDE INSULATING ALUMINUMCONDUCTORS Filed May 11, 1956 INVENTO'R Millard Z ,S'mzl t/z ATTORNEYUnited States METHOD FOR OXIDE INSULATING ALUMINUM CONDUCTORS Millard F.Smith, Westport, Conn. Application May 11, 1956, Serial No. 584,325

6 Claims. (Cl. 148-63) This invention relates to a method and apparatusfor insulating metal strip. More particularly, the invention relates toa method and apparatus for insulating metal foil, such as aluminum, byoxidizing the surfaces thereof.

Small electrical coils, such as inductance coils, may be Wound frommetal strip, one material which has been used therefor with some successbeing aluminum foil. Such foil in strip form is ideally suited for themaking of small coils where space is at a premium, but in the pastdifliculty has been experienced in prope ly insulat ing the surfacethereof. Heretofore attempts have been made to insulate aluminum foilstrip by the use of various varnish coatings but these were founddifficult to apply and control in thickness. The resulting coatings wereusually found to be too thick resulting in fractures and imperfectinsulation as well as excessive use of space. Also, the edges of thisaluminum foil strip are slightly irregular or ragged and it was founddifficult to cover these completely with the varnish, making forimperfect insulation. Aluminum oxide is known as a good electricalinsulator and thus attempts were made to insulate aluminum foil strip byoxidizing the surface. However, in the past attempts to do so met withdifiiculty because the oxide was often too thin and hence easily rubbedoff or too thick, resulting in coating fractures. When aluminum foil isexposed to normal atmosphere, an uneven film of aluminum oxide formscontaining many impurities resulting from the action of various gases onthe strip. The insulating properties of the film suffer from thepresence of such unevenness and impurities which also inhibit furtheroxidation to form effective insulation. Consequently, if any of suchoxide was on the surface of the aluminum before the oxidation process animperfect insulating coating was bound to be the result.

Accordingly, one of the objects of this invention is to provide a methodof insulating foil strip, such as aluminum, resulting in an insulatingcoating free from defeet and capable of forming electrical coils.Another object of this invention is to provide a method of the abovecharacter in which a continuously moving aluminum strip is oxidized withan insulating coating of substantial uniform thickness. Another objectof this invention is to provide a method of the above character whereina foil strip may be continuously and cheaply oxidized for purposes ofinsulation. Another object of this invention is to provide a method ofthe above character in which the thickness of the oxide coating may beautomatically and uniformly controlled. Another object of this inventionis to provide a method of the above character which will result in adurable coating well able to withstand the winding operation. Anotherobject of this invention is to provide an apparatus in which foil stripssuch as aluminum may be continuously and cheaply oxidized with a durablecoating of controlled thickness. Other objects will be in part obviousand in part pointed out hereinafter.

The invention accordingly comprises the several steps and the relationof one or more of such steps with respect to each of the others, and theapparatus embodying fea tures of construction, combinations of elementsand arrangements of parts which are adapted to effect such steps, all asexemplified in the following detailed disclosure aud the scope of theinvention will be indicated in the claims.

Referring now to the drawings in which is shown one of the variouspossible embodiments of this invention,

Figure 1 is a perspective view of a roll of aluminum foil of the type tobe oxidized by the method and apparatus described herein.

Figure 2 is a fragmentary plan view on a greatly enlarged scale of aportion of the metal strip to be treated according to the methoddescribed herein, and

Figure 3 is a diagrammatic sectional view of the ap paratus which may beused in the practice of my method.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

Generally speaking, my process utilizes aluminum foil strip which isusually received from the fabricator in large rolls such as illustratedin Figure 1. From such rolls small continuous strips of foil may be cutin any convenient manner and continuously run through the apparatusshown in Figure 3 to oxidize the surface thereof. This is done prior toentering Winding apparatus of conventional design for automaticallywinding electrical inductance coils or the like. Thus, the strip fromthe roll is passed through a chemical bath where all foreign matter,such as grease and oxides, is removed from the surface thereof. Afterthis it passes to a chamber for thorough drying and then is exposed toan ozone-containing atmosphere, preferably produced by ultravioletradiation, to form very quickly a continuous aluminum oxide coating overthe entire surface and edges of the strip thereby providing an excellentelectrical insulating cover for the strip. The strip then passes to thewinding equipment for formation into the desired coils.

More specifically the aluminum strip to be treated is cut from a rollgenerally indicated at 10 in Figure 1, and this may be achieved in anydesired manner. For example, the roll may be vertically sliced todesired thickness and each resultant small roll processed in the mannerto be described. On the other hand the entire roll may be mounted in theapparatus for processing and suitable mechanism provided forcontinuously cutting a small strip of the desired width from the largeroll to be fed through the processing apparatus.

In practice it has been found that even when the strip of foil is cutwith great care the resultant edges of the strip are somewhat irregularor ragged as indicated at 10a in Figure 2. Because of suchirregularities it has been found in practice that it is diflicult tocompletely cover such strip with an insulating coating. Theirregularities tend to protrude through varnish coatings and certainother types of chemical coatings used in the past. My improved methoddescribed herein assures a continuous coating throughout the strip.

Referring now to Figure 3 a standard 12 supports a roll 14 of aluminumfoil strip on a shaft 16. Suitable equipment (not shown) may be employedfor rotating the roll at a desired rate of speed to feed the strip 18therefrom to a tank, generally indicated at 20. As previously mentioned,roll 14 may be of considerable length and thus associated with suitablecutting equipment for cutting a narrow continuous length of strip 18therefrom. On the other hand, roll 14 may comprise a narrow strip of thedimensions used in forming these miniature electrical coils.

Strip 18 is fed forwardly or to the right as viewed in Figure 3 overroller 22, under rollers 24 and 26, and over roller 28. Rollers 22, 24,26 and 28 may be driven as desired at a proper speed for continuouslyfeeding strip Ice Patented Feb. 25, 1958 18 through a chemical bath intank 20. This chemical V winding of electrical coils. The continuousformation of 7 bath may be of any desired composition suitable for reaninsulating oxide coating of substantially uniform thick- 7 movingforeign matter such ;as grease, oxides and im- 7 ness makes for a verycheap way'of making small elecpurities from the strip withoutattackingthe metallic foil;. trical coils. l a e one of-the'arnines may be. usedforthispurpose; It will thus be seen that the objects set forth above,fl

T'Strip 18 passes from roller 28 through "the" processing 7 among thosemade apparent from the preceding clescripchamber generally indicated at30; Generallyspeaking, j tion, are efiiciently attained .and, sincecertain changes chamber-30 includes apparatus for firstthoroughly dryingmay bemade in c rrying ou the above m tho nd in he impurities whichprevent the formation ofa'nfefiectrveiin- 0 '2. The c a the strip, andthen subjecting it to ultra-violetjradiation'to 'COHSIfllctiOnlset:fdifli witholitidepafiilig fl'dlii th $501331 form an'oxide coatingthereon.

0f the invention, it is iritended that all matter contained The stripenters'the chamber30lthrough an opening, in' the above description orshownin the accompanying over and suitably dispdsed'to'wipefboth surfaces'ofi the limitingzsense. strip 18 as it move's'into the'jchamber.The strip then r I clalm:

passes between infra-red lamps 38 extendingfrorn the 1. Inamethod ofrctliilir i g oxide insulated aluminum a ,top of thechamber and suitablysecured thereto anfdflamps fiondllflor, the p j f f d Said 601161110821a 0011 upp neat on "a Shelf Q "-1i1 "4 z, 1n an atmosphere containingnascentroxygen to' remsulate Preferably the atmosphere .atathiis pointin itheinterior of 3335 qf i ai e s fip Where. Cracking ot :theoriginali the chamber is kept substantially free fr m .w nd oxide r u lq a a V V r nation aenneagn'e ain; 1 L n when. sate sulating'film. lliacco'mplishediri anez'en -containing at Preferablyj the stripnext-passes between' ultra-violet mospherei to 1' f- I: ll r i lampsor'other ozone producingapparatus-genera y in; 3. The Sc r'fibinatioiidefinedjini claim 1in vvhich said dicated at 44 and 46' and its surfacesare therebyfoxidi ti. i di g Is s acc'Q hpl jfihcdlinithe presence ofultra- 1 V The presence of the ozone i this portion of thech' 4 her iQl't radiation h A 1 h w h mt fw 1 i -n min mtq ndvstot V has beenfound toaccelerate the oxidation pr theirgit has been found inpractice' thatultra-v ation forms an oxide coating 'ove'rgthejentire su essentially'niatter' lrorn the "sur ces of said strip 18including the ragged edgesthereof. conductor d conduct r oxi ing- .said conf .this oxide coatingis of substantially uniform} and substantially free'fr'omlimpuritiesdher Q in an economical 'fa'shionadura'ble afidpraetiinsulating covering 'for the 'strip.

i ventionalwinding equipment illustrativelyfind .such breakage,agnewloiide coating is forrried ofhfth'e breakage is repaire'dibe'foreth cracked pitiohfisieoyrefcl e The strip then ente rsfa compartment 48cohtaiiiin conmospherel.w

for automatically forming electrical inductance cor s' or windingste'plis 1n thefirSpceofi ultrathe like. It has been found inpr'acti'cethat there maybe violet radiation. V a I r r a some cracking of theoxide coacting' due toth'e'behdin of r V i T a i E 1 the strip duringwindingf Accordingly I 'have' to diit V Referencestli ted thedileof thlspatent preferable to include in compartment 48, nu 'U rTgpsIarns,PATENTS ductor to insulate thesurfacfe" thereof, and Winding saidconductor intoafcdilj inItlie' presenc o'fzna scent ortygenf 7 o v o .5w h i Winding t s aq bfii'p i h -i z nesnt a rf a 59' 6. Thecornbinatioii 54 411 I lamps 52 for direc'ting ultra-Violet radiationagar t v a I e I i a 1, 2 5 May 10.1927 stnp as 1t 1s bemg wound mto0011. Thus, 1f there is any 7 9 p strip while it 'isbeingfweundtomaintain'thedesired'elece 5' trical insulation. Thjozorieprdduced by hemtram le V lampsi forms such new coati very, rapidly; so that, thjef byanother portion of the'eoil; c Accordingly; itcan 'be seen hitllhavegprevraeaa d Ple and l mail-16d. bl/M5195 M 41* vol. 1 pages 262-272pages 27'2 re1i'ed on. Fourth ed. sulating coatmgon anali rr numfoilstrip or ithelike in s r 1 A r v z pub. 1911. Filed November 13, 1951. 1V V a continuous fashion S0. that 1t may heutihzedm the. g

5o flRoscoe and. Schrolemmer: Trea'tis e on' Chemistr-y,

1. IN A METHOD OF COILING OXIDE INSULATED ALUMINUM CONDUCTOR, THE STEPOF WINDING SAID CONDUCTOR INTO A COIL IN AN ATMOSPHERE CONTAININGNASCENT OXYGEN TO REINSULATE THE AREA OF SAID STRIP WHERE CRACKING OFTHE ORIGINAL OXIDE INSULATION HAS OCCURRED.